It is known that the utilization of perfluoropolyethers as lubricants does not prevent the formation of rust on the surface of ferrous materials even if they are coated with an oil film, when moisture is present. The reason resides in the high permeability to gases, to vapors, and among these also water vapor, exhibited by perfluoropolyethers (PFPE).
PFPE utilizable for formulating lubricating oils and greases are broadly known on the market, such as, e.g., FOMBLIN.RTM. (produced by Montedison), KRYTOX.RTM. (produced by DuPont), DENNUM.RTM. (produced by Daikin), and the like.
As is well known, PFPE's are very difficult to enter into addition reactions, because a characteristic thereof is the absolute immiscibility with most chemical compounds. This in turn makes it impossible to use as additives the products which are usually employed for mineral oils traditionally utilized as lubricants and which, conversely, can easily enter into addition reactions, thus giving rise to mixtures which are sufficiently stable in the long run.